This invention relates to superconducting devices, and, more particularly, to a microbridge superconductor device incorporating a high-temperature superconductor material.
High-temperature superconductor materials are those having a normal-to-superconducting transition temperature, also known as T.sub.c, of more than about 77 K., the boiling point of liquid nitrogen. At temperatures below its T.sub.c, the superconducting material exhibits no resistance to the passage of electrical currents. The discovery of high-temperature superconductor materials has led to the possibility of many new applications of superconductors, because of the lower cooling and insulation requirements of the high-temperature superconductors as compared with conventional low-temperature superconductors.
The most important high-temperature superconductors discovered to date have been complex oxide compounds. These materials may be fabricated by depositing a thin film having the required composition of the metallic elements and either simultaneously or subsequently oxidizing the thin film to the required oxidation state. As an example, one of the most important of the high-temperature superconductor materials is YBa.sub.2 Cu.sub.3 O.sub.7-x, where x is small, typically on the order of 0.1.
To utilize the high-temperature superconducting materials, they must be fabricated into devices and products. An initial step in this utilization is to determine whether the high-temperature superconductors can be directly substituted for conventional low-temperature superconductors. To make this determination, an existing device that utilizes the well-known low temperature superconductors is constructed, substituting the high-temperature superconductor materials for the low-temperature superconductor materials, and its operation is evaluated. For example, in one application it is desirable to construct a thin-film microbridge superconducting device having Josephson junctions therein for use in manufacturing a detector such as a superconducting quantum interference device (SQUID). A SQUID made with a high-temperature superconductor in the Josephson junctions could be operable at temperatures as high as the T.sub.c of the superconductor, which is above 77 K., and therefore could be used in numerous applications that do not require cooling to near-absolute zero.
U.S. Pat. No. 4,454,522 discloses a thin-film microbridge superconducting device in which superconducting layers are deposited upon a stepped substrate. A layer of normal material (that is, not superconducting at the temperature of operation of the superconducting layers) is deposited overlying the superconducting layers. The gap between the superconducting layers along the step creates a microbridge that is the basis for a Josephson junction. The superconducting layers can be further patterned to produce a loop and leads, thereby creating a SQUID.
Unfortunately, the approach of the '522 patent is intrinsically not suited for producing an operable SQUID utilizing the anisotropic high-temperature superconducting materials such as those of the complex-oxide type. There nevertheless remains a need for a thin-film microbridge and a fabrication technique for its production. The present invention fulfills this need, and further provides related advantages.